start relay for a small fan motor question

[goodwrench]

I have a desa made propane torpedo heater. It has 1/8hp fan motor on it with a relay of sorts to work the start circuit. Well long story short when i plugged it in the fan was stuck. Got that fixed then wouldn't start unless i spun it. Finally narrowed it down to start relay and discovered a burnt contact. Got it fixed and taped back together and it works. But i am trying to figure out how this thing works. the main power wire comes to the relay, runs through a coil of wire wrapped around a plunger and out the other end of the coil of wire onto the motor. The start wire is connected to the incoming hot by way of the contacts inside it. There is no connection when there is no power applied. When you turn on the motor the relay energizes the start windings momentarily, then deenergizes the start windings. I can see how it energizes, current passing through the coil of wire = electromagnet and pulls the contacts together, but how does it release? I am wondering if it is something to do with the amperage going through the coil of wire? When it first starts it pulls like six amps through the coil, then drops to like two. Anybody know? I would love to understand how this thing works, and can't find the info..

Later!!! chris

 

[larry_g]

I believe that is called a potential relay. Searching that term I found


A potential relay operates on the voltage potential created by the induced voltage in the starting winding of the motor. It is an electromagnetic switch whose coil is wired directly in to the motor circuit. When power is applied to the circuit, the motor starts . As the motor attains its running speed the start winding acts as an auto generator and the voltage potential produced energizes the relay coil which cuts out the start capacitor and the start winding . The start winding still acts as an auto generator , however , and continues to produce enough power to keep the relay energized.




Read more: http://wiki.answers.com/Q/How_potential_relay_works_in_refrigeration#ixzz16vXEmyxC


Maybe a better site is

http://www.geindustrial.com/cwc/Dispatcher?REQUEST=PRODUCTS&pnlid=3&famid=1&catid=190&id=pr
lg
no neat sig line

 

[hidollartoys]

I believe this is a "current sensitive" relay. Contact is pulled in when the current in the coil reaches a predetermined current level and drops out when the current drops below a minimum threshold. A little different than a voltage activated coil.